The present invention is related to a motor driving device and a driving method of the same.
There are various motors such as a stepping motor, a direct current motor or the like existing in motors. For example, a stepping motor is used for, for example, operating a paper feeding portion of a copy machine or a printer or a reading portion of a scanner.
FIG. 12 shows an H-bridge circuit used in the conventional stepping motor driving device. The H-bridge is, for example, arranged at a front section of a stepping motor and configured as a circuit portion for directly driving the stepping motor. The H-bridge includes P-channel Metal Oxide Semiconductor (PMOS) transistors Q11, Q12, and N-channel Metal Oxide Semiconductor (NMOS) transistors Q13, Q14. Diodes D11, D12, D13 and D14 are configured to form a body diode of each transistor. If the node for connecting the transistor Q11 and the transistor Q13 is set as X, and the node for connecting the transistor Q12 and the transistor Q14 is set as Y, a motor coil L1 is connected between the node X and the node Y. In addition, the motor coil L1 indicates one phase. In the situation of two or three phases, two or three motor coils L1 are prepared, respectively. In this specification, one phase is shown for convenience of illustration. In this specification, only one phase is illustrated, and the driving actions for other phases can also be illustrated in the similar manner so as to be omitted.
The electric current path entering the H-bridge circuit is switched for performing the control of activation, rotation direction switch and stop of the stepping motor. In other words, a power supply mode and a electric current decaying mode are distinguished according to the electric current path entering the motor coil L1, wherein it has been known that the electric current decaying mode includes a slow decay mode, a fast decay mode and a mix decay mode consisting of the slow decay mode and the fast decay mode.
FIG. 12(a) shows the on-state and the off-state of each transistor and the electric current path of the H-bridge circuit while switching from the power supply mode to the slow decay mode. By using the arrow symbol (→), it is indicated as the power supply mode before the arrow symbol, and it is indicated as the on-state or the off-state of each transistor in the slow decay mode after the arrow symbol. The electric current entering the motor coil L1 in the slow decay mode is indicated by the symbol i10a. The electric current i10a flows when the transistors Q11, Q12 are turned off and the transistors Q13, Q14 are turned on. At this time, the electric current i10a circularly flows in the path (transistor Q13→motor coil L1→transistor Q14→transistor Q13). In addition, the power supply mode is performed for rotating the stepping motor at a specified rating; meanwhile, the electric current i10 is supplied from a power source Vpp to the path (transistor Q11→transistor Q14). At this time, the transistors Q11, Q14 are turned on, and the transistors Q12, Q13 are turned off.
FIG. 12(b) shows the on-state and the off-state of each transistor and the electric current path of the H-bridge circuit while switching from the power supply mode to the fast decay mode. By using the arrow symbol (→), it is indicated as the power supply mode before the arrow symbol, and it is indicated as the on-state or the off-state of each transistor in the fast decay mode after the arrow symbol. The electric current entering the motor coil L1 in the fast decay mode is indicated by the symbol i10b. The electric current i10b flows when the transistors Q11, Q12 and Q14 are turned off and the transistor Q13 is turned on. At this time, the electric current i10b flows in the path (transistor Q13→motor coil L1→transistor Q12). Meanwhile, regenerative current flows into the body diode D12 of the transistor Q12, but the transistor Q12 can be in the on-state at this time. In addition, the electric current i10b flowing into the motor coil L1 in the fast decay mode and the electric current i10 flowing in the power supply mode are in the opposite directions, i.e. the electric current i10b flowing toward the power supply Vpp.
FIG. 13 schematically shows the waveforms of the electric current flowing into the motor coil L1 when the electric current is decaying in the slow decay mode and the fast decay mode.
FIG. 13(a) schematically shows the waveform of coil current i10s flowing into the motor coil L1 in the slow decay mode. For convenience of illustration, the periods P1, P2, P3, P4 and P5 are shown along the time axis, respectively. The period P1 is the power supply mode, which controls the coil current i10s flowing into the motor coil L1 to gradually approach a reference current value IREF. When the coil current i10s reaches the reference current value IREF, the power supply mode is ended, and the period P2 enters the slow decay mode. When the specified time set for the slow decay passes, it enters the power supply mode in the period P3, again. The coil current i10s is controlled by repeatedly performing a series of actions, i.e. raising the coil current i10s to the reference current value IREF in the periods P3 and P5, and switching again to the slow decay mode in the period P4.
In the slow decay, when the coil current i10s is reduced (decaying), the voltage applied between two ends of the motor coil L1 is decreased, and the regenerative current is stably decreased. Hence, the current ripples become small, which is favorable to torque of the motor. However, in a region of small electric current, the motor coil is easily affected by the increased output electric current caused by the deterioration of electric current controllability or the counter electromotive force of the motor driven by high pulse rateat a half-step mode or a quarter-step mode. Hence, it would occur that the coil current i10s fails to follow the change of counter electromotive force and thus the electric current waveform deforms, resulting in the poor condition that the vibration of the motor is increased. In addition, if the electric current exceeds the predetermined electric current due to the influence of the counter electromotive force, deterioration may occur to the stepping motor or an integrated circuit (not shown) for driving the stepping motor in the predetermined time.
FIG. 13(b) shows the waveform of coil current i10f in the fast decay mode. Like FIG. 13(a), the periods P11, P12, P13, P14 and P15 are shown along the time axis, respectively. In the periods P11, P13 and P15, the motor coil L1 is supplied with the electric current in the power supply mode, and the coil current i10f is raised. In the periods P12 and P14, the fast decay process is performed, and thus the coil current i10s is reduced. The power supply mode and the fast decay mode are alternatively switched at the predetermined time.
In the fast decay, since the regenerative current is dramatically reduced, the deformation of the electric current waveform in the high pulse rate driving can be alleviated. In other words, in the fast decay, the advantage for improving the followability to the counter electromotive force, which cannot be expected in the slow decay, can be obtained. However, since the ripple of the coil current i10f becomes larger, the average electric current is decreased, resulting in the situation that the motor torque is reduced, the power loss of the motor is increased, and thus heat is increased.
FIG. 13(c) shows the waveform of coil current i10m in the mix decay mode. The mix decay is a electric current decay manner that eliminates the poor situations in the slow decay and the fast decay, and is a electric current decay manner for switching the slow decay and the fast decay during the electric current decay period. Generally, in the situation that the mix decay is applied, the determined ratio is generally used for switching the slow decay and the fast decay in the predetermined decay time.
In FIG. 13(c), like FIGS. 13(a) and 13(b), the periods P21, P22, P23, P24, P25 and P26 are shown along the time axis, respectively. The periods P21 and P24 are in the power supply mode, in which the motor coil L1 is supplied with electric current in the specified path. In the power supply mode, the coil current i10m is raised. The periods P22 and P25 are in the slow decay mode, in which the coil current i10m is gradually decreased. The periods P23 and P26 are in the fast decay mode, the coil current i10m is reduced faster than in the slow decay mode. In this specification, the continuous time of the periods P22 and P25 (slow decay period) is the predetermined time Tms, and the continuous time of the periods P23 and P26 (fast decay period) is the predetermined time Tmf, respectively. The length relationship between the time Tms and the time Tmf is not limited. In addition, the ratio of the time Tms to the time Tmf can be fixed according to the integrated circuit, and can be appropriately determined outside.
FIG. 14 is a diagram showing the poor situation which may occur in the slow decay and the fast decay in FIGS. 12 and 13, and showing the changes of the coil current i10n flowing into the motor coil L1 over time. FIG. 14(a) shows the overall situation of the electric current i10n flowing into the motor coil L1, and FIG. 14(b) is an enlarged diagram showing the electric current i10n1 around the time at which the coil current i10n reaches the reference current value IREF, i.e. the electric current i10n1 around time T61 in FIG. 14(a).
FIG. 14(a) shows the status that the coil current i10n is raised at time T60 and raised more during time T61˜T62 (i.e. the late stage of the pulse duration Tp). Herein, the reason causing the occurrence of the counter electromotive force, i.e. the reason of the rising coil current i10n is illustrated by using FIG. 14(b).
FIG. 14(b) is a schematic view prepared for illustrating the reason of the coil current i10n exceeding the reference current value IREF. Generally, when the transistors Q11˜Q14 of the H-bridge circuit shown in FIG. 12 are turned on or turned off, the spike noise occurs. Due to the influence of the spike noise, the poor situation that the coil current i10n1 cannot be precisely detected, and thus in order to prevent the erroneous detection of the coil current i10n flowing into the motor coil L1, the initial power supply is usually mandatory. In the slow decay, the coil current i10n1 should be reduced to a certain level; however, in the situation that the stepping motor has high vibration, the drop value of the coil current i10n1 becomes smaller due to the influence of the energy of the counter electromotive force. Herein, when the coil current i10n1 at time T611 reaches the reference current value IREF, it enters the slow decay mode. When the predetermined decay time reaches time T612, it is switched from the slow decay mode to the mandatory power supply mode, and the coil current i10n1 is raised.
In FIG. 14(b), time T612˜T613 for the mandatory power supply mode is relatively shorter, but in the situation that the drop value of the coil current i10n1 is small, it is possible that the coil current i10n exceeds the reference current value IREF during the mandatory power supply. The status that the coil current i10n1 exceeds the reference current value IREF during the mandatory power supply at time T612˜T613 is shown in FIG. 14(b). When the mandatory power supply mode is over at time T613, the detected coil current i10n1 is more than the reference current value IREF, it enters the slow decay mode again, and the coil current i10n1 begins to be declined. When the slow decay is over at time T614, it enters the mandatory power supply mode again and ends until time T615. Hence, overall, the coil current i10n is raised with time, and the original electric current decay process cannot be achieved.
The poor situations in the conventional electric current slow decay are illustrated in the above descriptions. In addition, for example, the following literatures are the background technical literatures related to the motor driving device of the present invention.
The patent literature 1 discloses a driving control device of a stepping motor for performing a first mode to increase coil current, a second mode to decay the coil current, and a third mode to decay the coil current at a higher speed than that of the second mode. Further, in the paragraph 0027˜0031 of the patent literature 1, it is disclosed that mandatory charge (power supply) is performed irrespective of the level of the coil current and the level of the predetermined electric current.
The patent literature 2 provides the following motor driver circuit: in order to lower the damping vibration (decay vibration) of a stepping motor, a first decay rate and a second decay rate less than the first decay rate are mixed for setting a plurality of mixed decay rates.
The object of the patent literature 3 is to operate a stepping motor more quietly, and the patent literature 3 provides that according to whether the coil current reaches the target current value after the predetermined duration of power supply, the fast decay or the slow decay is selected for decay path in the duration of decay for performing the electric current decay.
The patent literature 4 discloses the following motor driving device: the current value detected by a detection portion is compared with a threshold value, and referenced on the comparison result a first decay mode with high-speed decay and a second decay mode with low-speed decay are selected.